IB-367 is an inhaled antimicrobial peptide capable of killing pseudomona aeruginoas, hemophilus influenza, and streptococcus pneumoniae. The specific aims are to determine the safety and tolerability of ascending multiple doses of inhaled Ib-367 in adult patients with cystic fibrosis; to obtain preliminary data on bacterial density in sputum; to obtain preliminary data on FVC and FEVI; and to monitor for evidence of systemic absorption of IB-367. A maximum of 40 patients is expected in 5 dose groups. They are randomized in groups of 8 (6 active, 2 placebo). each patient receives 5 doses over 3 days.